Improvement of biohydrogen production from rice straw hydrolysate by green-self-prepared nano-silica

Rice straw stands as a highly sustainable agricultural residue enriched in silica and carbohydrates. This study delves into the potential of rice straw, focusing on the impact of green-synthesized nano-silica particles on biohydrogen fermentation using Enterobacter aerogenes. Rice straw was subjected to three different leading pretreatments, i.e., organsolv, sulfuric acid, and sodium hydroxide, to decimate the lignocellulosic structure. In addition to these, sodium hydroxide was employed as a secondary pretreatment for the organosolv- and sulfuric acid-pretreated straw. Three distinct nano-silica particles were extracted from the liquor of alkali pretreatments and examined using XRD, XRF, FE-SEM, and DLS analysis. The solid fractions of pretreatment were enzymatically hydrolyzed and subjected to dark fermentation, achieving the maximum biohydrogen yield of 156.9 ± 2.0 mL per g total solids (TS) from the organosolv-sodium hydroxide pretreated straw. Further improvement of biohydrogen yield to 178.3 ± 4.2 mL per g TS was obtained by adding 200 ppm of nano-silica particles isolated from one-step sodium hydroxide pretreatment. Analyzing the metabolic products exhibited that nano-silica particles modified the metabolic pathway, leading to an increase in acetic acid production and a decrease in ethanol production. It was concluded that nano-silica particles isolated from untreated and treated rice straws have the potential to boost biohydrogen generation. However, the degree of improvement was dependent on the composition and structure of the nanoparticles.